Long-Term Habituation. Is it really a non-associative process?

TOMSIC DANIEL

Salamanca, Spain

Congreso; IX International Congress of Neuroethology; 2010

International Society of Neuroethology

KEY WORDS: Escape response, visual stimuli, in vivo intracellular recording, arthropod optic neuropils, context memory Symposium 8: Long-term habituation. Is it really a non-associative process? Daniel Tomsic. University of Buenos Aires-CONICET. Argentina. Habituation is commonly classified as a nonassociative form of learning because it is assumed to be governed solely by the parameters of the habituating stimulus, in the absence of associations with other stimuli. Such a general assumption may be wrong. As proposed by Allan Wagner short-term habituation (STH) could be entirely nonassociative while long-term habituation (LTH) may entail associations with the contextual environment. But, because the vast majority of studies concentrated on STH, the notion that habituation is purely nonassociative is deeply embedded in the literature and in people’s mind. In my talk I will summarize results from an extensive program aimed at investigating the reduction of the escape response upon repeated presentation of a visual danger stimulus in the crab Chasmagnathus. Presentation of the stimulus without intertrial intervals (continued training) renders only STH. High frequency stimulus presentation (massed training) results in intermediate-term (1 day) habituation (ITH), whereas low frequency stimulation (spaced training) results in long-term memory (>5 days). LTH, but not ITH, is protein synthesis and context dependent. Experiments show that in fact, LTH is determined by an association between a memory of the habituating signal stimulus (signal memory, SM) and a memory of the context (context memory, CM). In vivo intracellular recording during learning allowed the identification of neurons from the crab’s brain that subserves every attribute of the SM, but they do not support the CM or the context-signal memory association (CSM). Our studies in Chasmagnathus illustrate that STH, ITH and LTH of the escape response (to the same visual stimulus) involve different neural substrates and mechanisms. These and further studies show that the commonly accepted definition that habituation is a simple nonassociative form of learning is misleading.